The present invention relates to a method of coating the inner wall surface of a pipe in a pipeline, in particular a gas pipe, with a sealant supplied as foam into the pipe, thereby to repair defective portions of a pipe which causes a gas leak, or to prevent the pipe from a gas leak.
A method of coating the inner wall surface with a sealant has a first step of filling the inside of a pipe in a pipeline with a sealant, and a second step of discharging any surplus sealant to the outside of the pipe. On the first step, the pipe is filled with the sealant for a predetermined period of time, thereby assuring that the sealant penetrates to the defective portions of the pipe which are likely to cause a gas leak, as well as providing sufficient time for the sealant to adhere to the inner wall surface of the pipe. On the second step, air is blown through the sealant filled pipe to discharge any surplus sealant from the pipe, while permitting the sealant which has adhered to the inner wall surface to remain on the inner wall of the pipe.
According to such a conventional method, however, the working efficiency is inevitably low in that the charging and discharge of the sealant are made in the two steps respectively. Furthermore, such a conventional method is uneconomical in that more sealant is used than is necessary to coat the pipe. Therefore, a lot of time is required for charging the pipe with sealant.
Moreover, during the coating of the inner wall surface with sealant, a portion of the charged sealant liquifies to increase the discharge resistance, so that discharge takes quite a lot of time.
In addition, the step of switching operation requires much time and, if one apparatus is constructed to handle these two steps, the whole structure inevitably becomes complicated.